Patent GB-671635-A (GB)
Title: Hydrocarbon conversion process for producing unsaturated hydrocarbons, particularly ethylene
IPC: C07C11/02
Filed: 1947-10-21
Abstract: Low-boiling unsaturated hydrocarbons are made by preheating a stream of hydrocarbon material capable of yielding unsaturated hydrocarbons by splitting to an elevated temperature precluding cracking, injecting high-temperature steam into the preheated hydrocarbon stream, rapidly heating the mixture predominantly by radiation while flowing in a single stream through a first zone of radiant heating to a conversion temperature of at least 600 DEG  C., and during said rapid heating effecting complete vaporization of the mixture with a minimum of cracking, dividing the resultant high-temperature stream into a plurality of substantially equal streams, supplying these to a second and separately controlled zone of radiant heating and heating them therein, predominantly by radiation, at substantially the said conversion temperature for a controlled conversion period within which a major portion of the hydrocarbon material is converted into a normally gaseous product consisting predominantly by weight of unsaturated hydrocarbons, discharging the conversion products from the second zone of radiant heating and arresting further conversion thereof by quenching with a relatively cool quenching liquid. Generally the charge is preheated at preferably below 325 DEG  C., the steam is in a super-heated state and at higher temperature than the hydrocarbon, preferably 550-800 DEG  C., and is preferably in a proportion of 0.1 to 0.6 parts by weight per part of the latter, the temperature of the first zone and conversion temperature is preferably 650-815 DEG  C., the conversion time is usually not more than 25 secs., more particularly 0.1 sec., at the higher and 6 secs. at the lower temperatures of the indicated range for a heavy oil such as gas oil but somewhat larger for more refractory stock such as naphtha, and the quenching liquid is water, or preferably a hydrocarbon oil, products being quenched to preferably below 425 DEG C. or more advantageously below 250-180 DEG  C.  In an illustration a gas oil or naphtha charge is preheated to 250-300 DEG  C. and combined with steam preheated to at least 650 DEG  C., preferably 740-760 DEG  C. in a ratio of 0.1-0.6 parts per part of hydrocarbon by weight, the mixture being passed through a heating coil in the first zone and rapidly heated to between 650-815 DEG  C., vaporized, divided, maintained at conversion temperature for 0.1-25 secs., quenched to preferably below 100 DEG  C. and fractionated. Particularly advantageous is the use of low-pressure conditions and pressures of 1.3-3 atmos. in the conversion zone and 3-5 atmos. in the previous zones are mentioned.  Products should be obtained at a pressure preferably only slightly above atmospheric.  Apparatus for use in the conversion is described and is also claimed in Specification 671,658 (see Group III).  In an example, paraffinic gas oil at 260 DEG  C. is mixed with steam at 1060 DEG  C. in proportions of about 0.3 parts of steam per part of oil by weight to give a resultant temperature of about 370 DEG C., rapidly vaporized at about 700 DEG  C., the pressure is reduced to approx. 2 atmos. and the charge converted at about 700 DEG  C. for approx. 1.5 secs., the products being discharged preferably at a superatmospheric pressure of 0.7 atmos., quenching being effected at 90 DEG  C. before fractionation to provide a substantial yield of ethylene, other products being propylene, butylene, butadiene and a very small quantity of acetylene; in a second example a paraffinic naphtha stream is used, preferably heated to about 760 DEG  C. after steam injection and conversion effected at this temperature for 1.5 secs. to yield ethylene and other unsaturated hydrocarbons.  Specifications 495,477, [Group III], and 560,195 also are referred to.ALSO:The Specification relates to the production of low boiling unsaturated hydrocarbons from paraffinic hydrocarbons by a cracking apparatus the subject of Specification 671,658. Specifications 495,477 and 560,195, also are referred to.